Accurate estimation of soil nitrogen (N) supply in the field is required to optimize fertilizer N management and to minimize environmental N losses in humid environments. Laboratory-based measures of N availability were evaluated as predictors of field-based indices of soil N supply within potato production systems. Pre-plant soil samples (0-15 cm) were collected from a series of forty treatments in established potato trials located in Atlantic Canada and Maine, USA. Total plant N uptake at topkill with no fertilizer N applied (PNU 0N ), PNU 0N plus soil mineral N to 30 cm depth at harvest and relative yield were considered as fieldbased indices of soil N supply. The potentially mineralizable N (N 0 ) was determined by aerobic Plant Soil (incubation at 25°C and periodic leaching for 24 weeks. A series of laboratory-based measures of soil N supply were measured in soil samples. Pre-plant soil nitrate or total mineral N at 0-30 cm depth was the best single predictor of PNU 0N (r=0.67 and 0.71, respectively) and relative yield (r=0.58 and 0.61). The ultraviolet absorbance of 0.01 M NaHCO 3 extract at 205 nm (NaHCO 3 -205) was suitable as a predictor of PNU 0N and relative yield in each growing season, however, the relationship between this parameter and PNU 0N or relative yield varied somewhat among years. A combination of pre-plant mineral N plus N mineralized in the first 2 weeks period of incubation after rewetting is proposed as a more robust measure of N availability compared with use of mineral N alone.

) applied either at planting according to normal grower practice, or at hilling, the latest time that granular fertilizer can practically be applied. Whole-plant dry matter and N accumulation were determined at topkill. Soil inorganic N content was measured to 30-cm depth at planting and at tuber harvest. Soil N supply (plant N accumulation plus soil inorganic N content at harvest with no fertilizer N applied) varied from 77 to 146 kg N ha -1 depending on the year. Crop N supply (soil N supply plus fertilizer N applied) was a better predictor of plant N accumulation than fertilizer N rate, and was used to remove the confounding effect of variation in soil N supply when making among-year comparisons for N use efficiency characteristics. Nitrogen uptake efficiency (NUpE; plant N accumulation/crop N supply) decreased with increasing rates of N applied at hilling N rate in 1999, which was a dry year, but was not influenced by at-hilling N rate in 2000 and 2001, or by at-planting N rate in any year. Nitrogen use efficiency (NUE; dry matter accumulation/crop N supply) and N utilization efficiency (NUtE; dry matter accumulation/plant N accumulation) decreased curvilinearly with increasing crop N supply in each year. Similar relationships between NUE and crop N supply, and between NUtE and plant N accumulation, among the 3 yr of the study suggest that these relationships are largely independent of seasonal climatic variation, and are primarily genetically controlled. Timing of N fertilization had no effect on any N use efficiency parameter, with the exception of reduced NUpE associated with split N application in 1999. This suggests that under rain-fed potato production in Atlantic Canada, timing of N fertilization has no significant effect on N use efficiency of Russet Burbank potato in years of adequate soil moisture, but NUpE may be decreased by split application of N in dry years.

This study investigated the value of using real-time monitoring of Phytophthora infestans airborne inoculum as a complement to decision support systems (DSS). The experiment was conducted during the 2010, 2011 and 2012 potato production seasons in two locations in New Brunswick, Canada. Airborne sporangia concentrations (ASC) of P. infestans were monitored using 16 rotating-arm spore samplers placed 3 m above the ground. The first cases of late blight (2010 and 2011) were detected 6-7 days after the first ASC peak, and all samplers captured their first sporangia within the same week (at 3-and 9-day periods). The cumulative ASC curve and the risk curves from two DSS (PLANT-Plus and Pameseb Late Blight) had the same shape but different magnitudes. In both locations, the negative binomial distribution fitted the data better than the Poisson distribution, which is indicative of heterogeneity, and based on Taylor's power law, the heterogeneity increased with increasing ASC. Therefore, the present results suggest that spore-sampling network devices may be a suitable approach for early detection of incoming inoculum and, when combined with DSS, represent a potential aid for targeting the optimal time to apply a disease-control product. In this context, cumulative ASC can be a counterweight to the DSS risk estimate: a high risk combined with significant ASC will trigger fungicide spraying. Moreover, spore sampling can be used to assess the efficiency of management strategies by means of examining the area under the inoculum progress curve.

G. 2005. Estimation of soil nitrogen supply in potato fields using a plant bioassay approach. Can. J. Soil Sci. 85: [377][378][379][380][381][382][383][384][385][386]. Soil N supply is an important contributor of N to crop production; however, there is a lack of practical methods for routine estimation of soil N supply under field conditions. This study evaluated sampling just prior to topkill of whole potato plants that received no fertilizer N as a field bioassay of soil N supply. Three experiments were performed. In exp. 1, field trials were conducted to test if P and K fertilization, with no N fertilization, influenced plant biomass and N accumulation at topkill. In exp. 2, plant N accumulation at topkill in unfertilized plots was compared with mineral N accumulation in vegetation-free plots. In exp. 3, estimates of soil N supply were obtained from 56 sites from 1999 to 2003 using a survey approach where plant N accumulation at topkill, and soil mineral N content to 30-cm depth at planting and at tuber harvest were measured. Application of P and K fertilizer had no significant effect on plant N accumulation in two trials, and resulted in a small increase in plant N accumulation in a third trial. Zero fertilizer plots, which can be more readily established in commercial potato fields, can therefore be used instead of zero fertilizer N plots to estimate soil N supply. In exp. 2, estimates of soil N supply were generally comparable between plant N accumulation at topkill and maximum soil NO 3 -N accumulation in vegetation-free plots; therefore, the plant bioassay approach is a valid means of estimation of plant available soil N supply. Plant N accumulation at topkill in exp. 3 averaged 86 kg N ha -1 , and ranged from 26 to 162 kg N ha -1 . Plant N accumulation was higher for sites with a preceding forage crop compared with a preceding cereal or potato crop. Plant N accumulation was generally higher in years with warmer growing season temperatures. Soil NO 3 -N content at harvest in exp. 3 was less than 20 kg N ha -1 , indicating that residual soil mineral N content was low at the time of plant N accumulation measurement. Soil NO 3 -N content at planting was generally small relative to plant N accumulation, indicating that soil N supply in this region is controlled primarily by growing season soil N mineralization. Use of a plant bioassay approach provides a practical means to quantify climate, soil and management effects on plant available soil N supply in potato production. 377-386. La quantité de N présente dans le sol apporte beaucoup au N dont les cultures ont besoin pour croître. Cependant, on manque de méthodes pratiques pour estimer couramment les réserves de N dans les champs. La présente étude devait établir si l'échantillonnage de plants de pomme de terre entiers n'ayant pas reçu d'engrais azoté juste avant le défanage donnerait une idée de la concentration de N dans le sol. Les auteurs ont effectué trois expériences à cette fin. Dans la première, des essais sur le terrain ont permis de vérifier si l...

) applied either at planting according to normal grower practice, or at hilling, the latest time that granular fertilizer can practically be applied. Tuber total and marketable yield, size distribution, specific gravity, fry colour and tuber concentrations of NO 3 , sucrose and glucose were measured. Increasing rates of N fertilization increased tuber yield and tuber size, increased tuber NO 3 concentration and decreased tuber specific gravity, but had little effect on tuber sugar concentrations or fry colour. Season-to-season variations in total tuber yield responses to N fertilization rate were attributed primarily to variation in soil N supply. Timing of N application had little effect on tuber yield, size distribution or processing quality under adequate soil moisture conditions. However, under dry soil conditions, split N application reduced tuber yield and tuber size. à la plantation, selon les pratiques en usage, ou au buttage, soit au dernier moment où l'on peut épandre un engrais granulaire. Les auteurs ont mesuré le nombre total de tubercules, le rendement en tubercules commercialisables, la répartition selon le calibre, la densité, la couleur à la friture et la concentration de NO 3 , de sucrose et de glucose dans le tubercule. L'augmentation du taux d'application des engrais azotés accroît le rendement en tubercules, la taille de ces derniers et leur concentration en NO 3 , mais réduit la densité et n'a presque aucune incidence sur la concentration en sucres ou la couleur à la friture. On a principalement attribué la variation saisonnière du rendement total résultant du taux d'application des engrais N à la variation des réserves de cet élément dans le sol. Le moment d'application a peu d'incidence sur le rendement en tubercules, la répartition selon le calibre ou la qualité à la transformation quand il y a assez d'humidité dans le sol. Quand le sol est aride cependant, l'application d'engrais N en plusieurs étapes diminue le rendement en tubercules et le calibre de ces derniers.